Abstract

Nanolayered coatings of ZrO2/Al2O3 and ZrO2/Y2O3 were prepared using pulsed sputtering to study the feasibility of stabilization of various polymorphs of ZrO2. These coatings were deposited at various substrate temperatures (350-700C), individual layer thicknesses (1.9-25.2 nm) and modulation wavelengths (, 9.6-32.7 nm). The cross-section of ZrO2 and Y2O3 coatings consisted of micro-columns whereas, the ZrO2/Al2O3 and ZrO2/Y2O3 multilayer systems exhibited a less columnar microstructure. X-ray diffraction (XRD) data showed that ZrO2, Y2O3 and Al2O3 coatings exhibited monoclinic, cubic and amorphous structures, respectively. For ZrO2/Al2O3 nanolayered coatings prepared at   13.8 nm, a tetragonal phase of ZrO2 was stabilized. In the case of ZrO2/Y2O3 nanolayered coatings prepared at 24.4 nm    9.9 nm, ZrO2 was stabilized in the cubic phase. Superlattice structure with satellite reflections up to 3rd order was observed for ZrO2/Y2O3 nanolayered coatings prepared at  = 9.9 nm. The formation of various polymorphs of ZrO2 was also confirmed using micro-Raman spectroscopy. XRD studies demonstrated stability of the tetragonal and the cubic phases of ZrO2 in the ZrO2/Al2O3 and ZrO2/Y2O3 multilayers, respectively up to 1100C in air. The maximum nanoindentation hardness values obtained for ZrO2/Al2O3 and ZrO2/Y2O3 nanolayered coatings were 30 and 28 GPa, respectively, which were very high as compared to the rule-of-mixture values. Detailed studies on elastic/plastic behavior of the multilayers indicated highest resistance to plastic deformation for the ZrO2/Al2O3 multilayers.